This invention describes an optical communications infrastructure for implementation on a flat semiconductor wafer, useable in Optical communications, switching, routing.
The explosion of the Internet, E-business, and multimedia applications has created a tremendous need for increased bandwidth. To address these demands, there has been considerable interest in creating micro-mirror arrays for optical networking applications that are capable of carrying vast amounts of date. Currently available sub-micron silicon CMOS fabrication technologies and micro-machining techniques provide the opportunity to create an intelligent cross-bar switch, based on micro-mirror arrays or other optical switching components, for optical telecommunications applications. The main benefit of merging these technologies on-chip is the capability of performing cross-bar switching between a number of optical telecommunications channels with low signal attenuation and in a very compact structure. The integrated switch system shall also be capable of detecting and identifying the data content of incoming optical channels, and re-configuring the switching pattern accordingly. The built-in intelligence of the system, together with its compactness and its low insertion loss, should make this device very attractive for a number of high-speed telecommunications applications.
In order to sample the incoming optical signals and to perform the switching according to the data content of each channel, the optical signals must be re-directed on an array of optical sensors which are built into the substrate. An optical beam splitter structure can be used for this purpose. Each optical sensor will continuously detect the incoming data stream and direct this information to a built-in decision and control unit. Based on the extracted information (for example data headers or specific patterns contained in the data stream), the control unit will identify the data content of each channel and re-configure the switch matrix accordingly. This capability offers truly adaptive switching between a number of incoming channels, where a change in data content of an incoming channel during operation will automatically result in re-direction of the outgoing channels. The conditions for signal recognition and re-routing of channels can be pre-programmed into the computational unit, based on a set of criteria for channel switching. In addition to these applications, there is an emerging area of optoelectronic information processing which is based on permutation networks. The availability of an intelligent optical switch array based on micro-mirrors could also have important implications towards the implementation of such novel architectures.
These new micro-fabrication technologies allow the fabrication of ultra small movable structures. This can be used for micromirrors which can be, for example, electrostatically actuated. Although the switching speed of micromirrors is not very high compared to electro-optical modulation, micromechanical structures have been considered for several applications such as projection displays, scanners, cross-connections of optical fibers and optical switches arrays. Micro-mirrors can be realized in silicon bulk micromachining, polysilicon surface micromachining and metal thin films. The most common actuation principle is electrostatic force which scales best with small dimensions, but electromagnetic, thermo-mechanical and piezoelectric actuation can also be applied.
One of the most advanced application in micro-mirrors arrays to date is the xe2x80x9cDigital Mirror Devicexe2x80x9d (DMD) which has been developed by Texas. The DMD is a micromechanical spatial light modulator array which consists of a matrix of tiny mirrors (16 xcexcm base) supported above silicon addressing circuitry by small hinges attached to support post. The pixel can be made to rotate about its axis by applying a potential difference between the pixel and the addressing electrode.
Building on the emerging technologies described above, it is an object of the current invention to disclose a novel method for the construction of high density optical switches that is simpler, more cost efficient, and allows for the construction of more complex systems on a single wafer than that was possible with conventional methods.
This invention discloses a novel method of manufacturing optical communications infrastructures that are implemented on a flat semiconductor wafer, and the optical devices that are made possible by this manufacturing process. This invention has the following characteristics which enable the efficient manufacturing of a combination of elements onto such a wafer: the inherent surface flatness, crystal purity and uniformity over a relatively large dimension for semiconductor wafers (i.e., 8-inch or 10-inch diameter wafers can be used in Silicon semiconductors); the low cost and wide availability of such wafers; and the ability to combine several types of elements onto the wafer, on a very dense scale, and in a highly repeatable and mechanically aligned manner.
Elements that can be fabricated onto the wafer include electronic components (e.g., transistors and conductors), mechanical components that are native to the wafer (e.g. alignment grooves, alignment pins, micro-mirrors, electromechanical actuators, optical waveguides, refraction-index changing optical switches, and diffraction gratings), mechanical or optical components that are foreign to the wafer (e.g., mirror sub-assemblies, external fiber optic cables, lenses, and diffraction gratings), and foreign electrical components (e.g., silicon or separately manufactured optical-to-electrical or electrical-to-optical converters).
A key use of this invention is for building dense (on the order of 10,000 by 10,000 on a 10-inch diameter wafer) N-by-M arrays of optical switches using various types of mirrors or optical switching mechanisms, organized in an N-by-M 2-dimentional matrix (xe2x80x9cswitching matrixxe2x80x9d) built onto a flat semiconductor substrate (such as Silicon), connected to N input fiber optic cables (or less if wavelength splitting is used on the wafer) and M output fiber optic cables (or less if wavelength combining is used on the wafer). The input and output fibers are optically interconnected to the switches via optical waveguides in the wafer.
This switching matrix on a wafer allows the optical coupling (connection) of any one of N inputs to any one of M output optical signal paths in any arbitrary combination. Additionally, the switching matrix allows for the following features: redundancy in routing paths as well as in fiber connections; the routing of a pilot optical signal for self diagnostics of the switching array; the routing of input signals to multiple output paths (i.e., multicasting); the routing of input signals to secondary non-intrusive functions such as: optical power measurement, performance monitoring, alternative wavelength decoding; the separation of individual wavelengths from each input fiber and its individual routing within the same matrix to any output fiber (as well as to the secondary paths, and multicasting); the optical combination of various wavelengths from one or more input fibers into the same fiber output; the provision to incorporate wavelength translation components within the switch matrix; automatic alignment of input and output fiber optical paths to the on-wafer optical signal paths; the ability to scale the matrix up (or down) in density, and scaling of optical waveguide dimensions using built-in 3-dimensional waveguides within the switching matrix; automatic one-step alignment during construction of all optical components and paths; the ability to incorporate control and monitoring electronics which are embedded within the wafer; the ability to add non-native optical and electronic components in a fully optically aligned fashion to the wafer material; the ability within the matrix to variably attenuate an input optical signal (either full fiber or sub wavelength); the ability to adjust the power levels in any number of 1-to-N routings of an input optical signal; the ability to insert optical amplifying elements within the switching element; and finally, the ability to cascade multiple switches for increased matrix size, or for the incorporation of additional secondary functions.
A key feature of the invention is that the optical paths are parallel, rather than orthogonal, to the xe2x80x9cworking surfacexe2x80x9d (in this case, the surface of the wafer). Implementations known in the art commonly use complex 3-dimensional structures to perform the switching functions from the input fibers to the output fibers, or, in case of the Texas Instruments DMD or LCD-on-Silicon graphics systems, the light path is orthogonal to the wafer (the mirror is flat on the wafer). Compare this to the instant invention, which uses flat 2-D structures on the wafer itself. By eliminating variations in the third-dimension because of the wafer""s flatness, the invention enables the fiber, optical waveguide, and optical switching elements to be inherently aligned to each other during fabrication by simply using conventional wafer-processing techniques (for the x- and y-dimensions).